There exist various known types of coupler fittings for attaching an electric metal tube (EMT) to an electrical installation such as an electric box or panel or for joining at least two electrical metal tubes in an end-to-end relationship. Such known coupler assemblies include a coupler body to which the electrical metal tubes are rigidly connected to the coupler body, e.g. as disclosed in U.S. Pat. Nos. 268,686; 3,976,314; 4,073,514; 4,091,523. Other known coupler assemblies include a coupler body wherein at least one connected electrical metal tube is permitted to telescope or slide relative to the coupler body or relative to another electrical metal tube fixedly connected to the coupler body, e.g. as disclosed in U.S. Pat. Nos. 5,141,258 and 6,715,803.
With respect to such known sliding or telescoping coupler assemblies, it has been noted that because of the relatively free or sliding relationship between the moveable electrical metal tube relative to the coupler body, the optimal electrical grounding effect therebetween is substantially diminished because of insufficient contact between the complementary surfaces of the movable electrical metal tube and the associated coupler body due to the required tolerance necessary to permit the desired telescoping between the moveable electric tube and the associated coupler body. Thus, the optimum desired amount of the electrical grounding effect therebetween is not achieved.
Additionally, problems have been encountered in grounding being diminished or compromised over time resulting in poor grounding. Additionally, movement of conduits or electric metal tubing during securing of the electric metal tubing has often led to poor sealing.
Efforts have also been made to improve continuity in electrical fittings or connectors. Nearly all of these efforts have been directed to increasing contact surface area. For example, U.S. Pat. No. 6,709,280 entitled “Fitting with Improved Continuity” issuing Mar. 23, 2004 to Gretz. Therein disclosed is a fitting for connecting a cable to an electrically conducting junction box having a sloped grounding tang in which the downward slope causes the fitting to be drawn tightly against the junction box wall. Another fitting is disclosed in U.S. Pat. No. 6,780,029 entitled “High Continuity Electrical Fitting” issuing Aug. 24, 2004 to Gretz. Therein disclosed is a fitting for connecting a cable to an electrically conducting junction box that has larger grounding tangs providing much greater surface contact area, thereby improving continuity and lowing millivolt drop.
While these prior techniques improve continuity they have done so by increasing surface area contact. While this may provide some improvement in continuity, there is a limit to the increase surface area contact that can be obtained in an electrical connector or fitting. Therefore, there is a need for a different approach in obtaining improved continuity or conductivity between the electrical conductor or fitting, the electrical box, or the cable. This has been a particularly difficult problem for telescoping coupler assemblies that inherently must have sliding surfaces.
Therefore, there is a need for a telescoping coupler assembly with improved grounding, sealing, and continuity.